By "contact adhesive" is meant herein an adhesive which is typically applied to two surfaces to be adhered together, dried to form clear film adhesive layers, and brought into contact with pressure so as to form an immediate, durable bond. Such adhesives are used, for example, in laminating plastic, such as Formica.RTM., to particle board for kitchen counter tops (high pressure laminate (HPL)) and for gluing foam to wood in sandwich panels. Once the contact adhesives are pressed together, the adhered pieces are to be ready for further processing, such as cutting; contact adhesives being formulated so as not to require adhesive curing to achieve the requisite bond strength.
Most contact adhesives, heretofore, have been solvent-borne. Low boiling point organic solvents as carriers for contact adhesives provide the advantage of rapid dry times, whereupon the workpieces may be contact-adhered very soon after application of the adhesive composition. Increasingly, however, organic-borne compositions are becoming disfavored for the volatiles they release both to the immediate workplace or the general environment.
Waterborne contact adhesives have been developed, Fastbond.RTM. adhesives produced by 3M being a prime example. While Fastbond.RTM. adhesives have met with considerable success, they are based primarily on neoprene latexes, a relatively expensive substance. Resistivity to high temperature of Fastbond.RTM. is less than desired. High-temperature resistance is important in a contact adhesive as the adhered workpieces may be subject to further processing, such as cutting, which may generate considerable localized heat and may result, for example, in delamination at the edges. Also, Fastbond.RTM., like most other waterborne contact adhesives, still contains some organic solvent.